The Five Love Languages by Gary Chapman
This is one of the most powerful books I have read on relationships. I recommend it and facilitate an exercise in my Blissology classes. Learning to love others in a way that they can feel instead of the ways that you feel love is paramount.
Here is a great blog on the basics taught in the book. http://dlcloe.wordpress.com/2013/04/16/the-five-love-languages-explained/